GEOLOGY OF THE NORTHERN ADIRONDACK REGION 283 



the south, the Chazy deposits rapidly thin out, and the forma- 

 tion was not deposited on the^south and west sides of the region 

 at all. Subsidence thereabouts must therefore have intermitted 

 during Chazy time and likely during the latter part of Beekman- 

 town time as well. In fact, the downward movement seems to 

 have been replaced by one in the contrary direction, bringing 

 above sea-level an area of considerable, though unknown, extent 

 to the south and west of the Adirondacks, a condition in which 

 it remained throughout Chazy time. The altitude above sea-level 

 must have been very slight, since the surface shows little sign of 

 wear. 



The Chazy basin then spread over the nOrth and east sides 

 of the region only, its open water connection being with the 

 eastern, and not with the interior sea, the extent of the latter 

 being considerably contracted during this time. 



Lowville limestone. This is a comparatively thin band of pure 

 limestone which directly overlies the Beekmantown on the south 

 and west sides of the Adirondacks, but does not appear at all 

 on the north and east. The Chazy elevation on the southwest 

 was terminated by depression, and at about the same time or 

 previously, elevation occurred, draining the sea from the Chazy 

 basin. The Lowville is plainly unconformable to the Beekman- 

 town surface, varies much in thickness and is wholly wanting 

 in places, evincing the irregularity of surface on which it was 

 laid down. 



The conditions under which the Lowville was deposited did 

 not permit the entrance of, or else were unfavorable to the life 

 of a marine fauna. If the former be the explanation, there must 

 have been a land barrier between it and the sea to the south; 

 if the latter, the cause is purely conjectural. Certainly the rock 

 is very barren of fossils for the most part. 



Black River and Trenton formations. Both the Chazy formation 

 on the northeast and the Lowville on the southwest are over- 

 lain by a series of limestone beds which are plainly of marine 

 origin, showing that following the Lowville, subsidence was 



